The present invention relates generally to signal acquisition probes for measurement instruments and more particularly to a probing tip formed on a non-conductive substrate.
A signal acquisition probe is used in conjunction with a measurement instrument, such as an oscilloscope, logic analyzer, spectrum analyzer and the like, for coupling an acquired test signal from a device under test (DUT) to the measurement instrument for analysis and display of the test signal. Signal acquisition probes have at least one electrically conductive probing tip formed of an electrically conductive material, such as copper, beryllium-copper, aluminum, steel, metal alloys, such as nickel-palladium alloy, and the like. The probing tips may be formed as conical nails or pins that taper to a point. Other tip configurations include bevels, wedges and the like.
The signal acquisition probe has probe head with an electrically conductive hollow tube having a substrate disposed therein. The substrate may be formed of ceramic or circuit board material and the like and has passive and/or active circuitry thereon to prevent loading of the test signal and for conditioning the signal for coupling to the measurement instrument. One end of the hollow tube has an insulating plug disposed therein with probing tip coaxially extending from the plug in both directions. The portion of the probing tip extending into the hollow body is electrically connected to the substrate. The probing tip may be electrically coupled to the substrate using spring loaded electrical contacts, electrically conductive fuzz buttons, wire bonding, soldering or the like. An electrically conductive cable is attached to the substrate for coupling the conditioned electrical signal to the measurement instrument. The overall bandwidth of measurement probes using metal probing tips is limited due to capacitive and inductive effects of the metal probing tips.
As the bandwidth of measurement increases, there is a corresponding need for measurement probes having equal or greater bandwidths. A major difficulty in designing very wide bandwidth measurement probes having bandwidths of 5 GHz and greater is the effects of capacitance and inductance of the probing tip or tips. One solution to this problem is to separate the probing tips from the active circuitry in the probing head of the measurement probe. U.S. Pat. No. 6,704,670 describes a wideband active probing system where the probing tip or tips of the probe are separable from a probe amplifier unit. A probe tip unit is connected to the probe amplifier unit via one or more probe cables for conveying signals received by a probe unit. Various types of probe tip units may be connected to the probe amplifier unit. The probe tip unit may contain circuitry ranging from conductor traces to various resistive, capacitive, and/or other electronic elements. An advantage of such a probe design is that it allows the placement of the substantially smaller probe tip unit onto difficult to reach contacts on a device under test instead of a larger measurement probe containing probe amplifier circuitry.
The probe tip unit may be single ended or differential and includes a hand-held differential browser having variable spacing. The hand-held browser allows a user to manually probe various points on the device under test. The probe tip unit may also have probe connection points for electrically connecting various types of probing tips to the probe tip unit. The probing tips are secured to the probe connection points of the probe tip unit by soldering or compression terminal connections. Various types of probing tips may be soldered to the probe connection points, such as resistors, SMT grabbers, wedge probe tips and the like.
U.S. Pat. No. 7,056,134 describes attachable/detachable probing tip system mountable on a probing tip member that is attached to a probe body via coaxial cables. The attachable/detachable probing tip system has a probe tip mounting member that receive various types of probing tips, such as wire leads extending from resistive elements and resistors with wire leads attached to electrically conductive traces disposed on flex-circuit material formed as probing arms. The probe tip mounting member has attachment arms that engage the probe tip member for securing and electrically connecting the probing tips to the probe tip member.
The above described probing tip systems allows the placement of damping resistors in close proximity to the probe contact point on the device under test using the wire leads of resistors. Placement of resistive elements close to the probe contact point on the DUT reduces the loading of the device under test at high frequencies and reduces the capacitive effects of the metallic resistor leads. Probe bandwidths as high as 20 GHz have been achieved using the above described probing systems.
There is a continuing need for signal acquisition probes with higher and higher bandwidths. This requires rethinking of how signal acquisition probes make electrical contact with test point on the device under test. Replacing the traditional metal probing tips, be it traditional metals tips or wire leads of resistors, is one alternative to increasing signal acquisition probe bandwidths into the 30 GHz range.